1. Field of the Invention
This invention is related to laser deposition or laser ablation of dielectric material on metallic substrates, especially to deposit a capacitive filter. This invention is also related to the use of capacitive filters in electrical systems and more particularly to the use of electrical connectors containing capacitive filters.
2. Description of the Prior Art
Filtered and shielded electrical connectors are commonly used to control electromagnetic interference (EMI) and radio frequency interference (RFI) in electronic circuits used in noisy environments. Susceptibility to external EMI must be limited both for the electronic systems to function properly and mandatory limits are also imposed for certain applications. Filter connectors are also used to prevent unwanted emissions from noisy circuits to the surrounding environment.
Perhaps the most common method of dealing with these problems is to introduce lumped filter components on printed circuit boards used in these electronic devices. Since filtering requirements are often determined only during testing and often after products are designed and produced, this approach typically means that printed circuit boards must be redesigned. In some applications printed circuit board real estate is limited and this requirement can cause other complications. Even where printed circuit board real estate is available, this band aid approach can cause significant delays. Even minor changes, such as the addition of one or more capacitors, can cause significant problems in applications using complex multilayer printed circuit boards. For these and other reasons, filtered electrical connectors provide a desirable alternative.
One common method for including filtering in electrical connectors is to mount an auxiliary printed circuit board subassembly, including capacitors and possibly other filtering components, on the connector. These auxiliary printed circuit boards are commonly designed for specific filtering applications. The filtered connectors provide probably the best way to address EMI problems because the connectors are generally located at input and output ports of electronic modules or components.
Typically these filter subassemblies are incorporated either in new connectors especially designed for the specific applications or in conventional electrical connectors, especially modified for filtering applications. This is especially true in automotive applications. However, not all applications have the same filtering requirements or the same connector configuration, thus limiting the economic advantage that can otherwise be realized by using standard commercially available connectors. Even in applications in which standard electrical connectors can be used, it has been common practice to provide filtering for all lines, even where noise is only a problem on certain lines. Subassemblies that add filtering to all lines are also inconsistent with applications in which some lines or individual circuits are ground rather than signal lines.
Surface mounted chip capacitors are currently used in may filtered applications. Dielectric material is screened onto a disposable surface to make surface mount chip capacitors. The screened material is then subjected to a drying and sintering process before the electrodes are plated. The high temperature sintering process precludes the use of low temperature substrates, such as copper and copper alloys, which are conventionally used for electrical contact terminals. One method of using standard surface mount chip capacitors for adding filtering to an electrical connector is to mount standard surface mount capacitors on a printed circuit board or other member. The printed circuit board is then mounted to the connector, typically at the rear of a connector, such as a pin header. and the capacitors are connected between the corresponding pin and a ground member, such as a metal shield. Another approach, represented by U.S. Pat. No. 4,682,129, is to form the capacitors on the substrate using a common technique, such as screen printing, to form conductive layers, or electrodes, as well as an intervening dielectric layer. Barium titanate is used to form the dielectric layer in that patent.
Barium titanate has also been suggested as a material to form a dielectric layer in field effect semiconductors in dynamic random access memory devices and for use in devices in super-conducting electronics. Laser deposition or laser ablation has been suggested as one method of forming the dielectric thin films for use in those applications.